1. Field of the Invention
The present invention relates to a range shift mechanism mounted in a vehicle or the like, and in particular, to a range shift mechanism (so-called shift-by-wire) interlocked with the operation of a range selecting mechanism, such as a shift lever, and controls, for example, a hydraulic control unit, to change over a shift range.
2. Related Art
A range shifter mechanism that changes the shift range of an automatic transmission conventionally includes a manual valve within a transmission and a shift lever provided in the passenger compartment and connected to the manual valve via a shift cable. The manual valve is positioned via the shift cable according to the operation of the shift lever by a driver.
In recent years flexibility in the location of the shift lever has become increasingly needed to respond to demands for increasing the degree of freedom in vehicle cabin design and in expanding derivative vehicle types from identical platforms. However, the shift cable which connects the shift lever and the manual valve has many layout restrictions and, accordingly, development of a range shift mechanism that does not use such a shift cable has been needed.
A range shift mechanism in answer to the aforementioned demands is proposed, for example, in Japanese Patent Laid-Open Publication (“Kokai”) No. 7-190180. The range shift mechanism disclosed in the Kokai 7-190190 includes an electric motor which transmits torque to a manual valve to operate the manual valve and thereby change the shift range. However, such a range shift mechanism may have difficulty in changing to a desired shift range due to, for example, failure of a position detecting sensor (position sensor) for detecting the target shift range, or difficulty in recognizing position with the sensor due to, for example, influences of noise or temperature.
In addition, the prior art range shift mechanism does not provide for situations such as fluctuations in the drive of the electric motor caused by large changes in ambient temperature. Fluctuations in the drive of the electric motor, in turn, translate into differences in the operating position of the manual valve, thereby causing difficulty in changing to the desired shift range.